As is known, plants exhibit their optimal qualities at the time they are harvested. In contrast, these qualities deteriorate very rapidly. It is important therefore to "stabilise" them in order to try to preserve as much as possible the essential and desired component of these properties.
As is known, the stabilisation of fresh plants is a process which aims to preserve all the initial properties of these products, from the point of view of the therapeutic active ingredients (alkaloids, trace elements, vitamins, essential oils, polyphenols and the like), as well as other properties such as taste, colour and odour.
Most generally, in order to stabilise plants, they are air-dried. Although very widespread, this technique exhibits numerous disadvantages essentially related to the slowness of the procedure which leads to degradation, decoloration and deodorisation. All the processes for stabilising plants known hitherto aim to inactivate the enzymes which they contain. As is known, in practice, the denaturation of enzymes is obtained at a temperature which is specific for each enzyme, most often at temperatures between 70 and 90.degree. C. Because of the poor thermal conductivity of plant tissues, some parts close to the surface heat up considerably whereas the temperature of the internal zones increases slowly. This is particularly distinct in the case of thick and ligneous organs.
In order to stabilise plants, that is to say annihilate the enzymes, processes which require the use of moist heat, water vapour, or even alcohol vapour, in particular ethanol, have hitherto essentially been used. Dry heat is hardly used because, as the temperature rise is slow, the enzymes unfortunately express their activity well before being destroyed.
The use of ultrahigh frequency currents on fresh or withered plants or for drying oleaginous seeds, for example of sunflower plants, in particular in order to improve the hulling of these seeds has already been proposed. These techniques have not been developed, probably because of their high cost as they require extremely long durations of treatment and have proved useful only for the treatment of seeds and not of plants.